A conventional socket generally includes a tubular body with a first recess in one end and a second recess in a second end of the tubular body. The first recess receives a driving protrusion of a hand tool such as a wrench and the second recess receives an object to be loosened or tightened. The socket is generally made by steel and has a high degree of stiffness so that when the socket contacts an object, the socket might scrub the object. U.S. Pat. No. 6,397,706 discloses a protective socket which includes an inner part made by softer material and an outer part which is made by hard material. The inner part is inserted in the outer part and one end of the inner part extends out from an end of the outer part such that when using the socket, the end of the inner part extending beyond the socket can be a protect device to contact the object without damaging the object.
However, it is noted that the inner pat has a smooth outer periphery and the outer part has a smooth inner periphery so that the inner part cannot be well positioned in the outer part. In addition, the inner part might be twisted during using the socket and disengaged from the outer part.
The present invention intends to provide a socket assembly wherein the inner part has ribs or grooves in an outer periphery thereof and the outer part has groove or ribs which are engaged with the grooves or ribs. By this way, the inner part is not disengaged from the outer part.